c# adding two lists in recursive return

Question

I am implementing recursive Median cut algorithm https://en.wikipedia.org/wiki/Median_cut and have problem, with my return it says "operator + can't be applied to operands of type List and List".

Here is my code so you get insight of what i'm asking about:

public static List<Color> Cut(List<Color> input,int n)
    {
        if (n == 1)
        {
            //creating List<Color> containing 1 color element which is
            //average of all colors from input and returning this 1 element
            //list ending our recursion
        }

        else
        {
            SortWithRespectToWidestChannel(input)
            int median = input.Count / 2;
            List<Color> l1 = new List<Color>();
            List<Color> l2 = new List<Color>();
            l1.AddRange(input.GetRange(0, median));
            l2.AddRange(input.GetRange(median, input.Count - median));

            return Cut(l1, n / 2) + Cut(l2, n / 2); // <---**here is problem**
        }

So do you know how can I resolve my problem? Thank you in advance.

Answer 1

Try this if You want to have all Colors in one list.

Change:

return Cut(l1, n / 2) + Cut(l2, n / 2); // <---**here is problem**

to

  var result = new List<Color>();
  result.AddRange(Cut(l1, n / 2));
  result.AddRange(Cut(l2, n / 2));

  return result;

Give me feedback if i correct thing about Your problem.